Gastrectomy Causes Bone Loss in the Rat: Is Lack of Gastric Acid Responsible?

Abstract

Total gastrectomy or resection of the acid-producing part of the stomach (fundectomy) in the rat induced a marked and rapid reduction in bone wet weight, ash weight, and density (expressed as ash weight in mg/mm³ bone). Bone volumes were also affected but not as much. The radius, sternum, tibia, and femur were studied. Three weeks after gastrectomy the bone ash weight was reduced by almost 30% and the density by more than 25%. Maximum bone loss (approximately 40%) occurred about 6 weeks after the operation. The bone loss after gastrectomy was somewhat greater than that after fundectomy, whereas antrectomy had a marginal effect only. The percentage trabecular bone volume, calculated from morphometric analysis of histologic sections of the tibia, was greatly reduced by gastrectomy (approximately 50%), somewhat less so by fundectomy, whereas antrectomy had little effect. We set out to study whether calcium malabsorption could explain the bone loss after gastrectomy. Gastric acid is thought to facilitate the intestinal absorption of ingested calcium by mobilizing calcium from insoluble complexes in the diet. The possibility that lack of acid might contribute to the bone loss after gastrectomy was examined in experiments in which the proton pump inhibitor omeprazole was given for 4–8 weeks at such a dose (400 μmol/kg/day) that acid secretion was blocked almost completely during the period of study. This treatment was without effect on bone. However, the possibility could not be excluded that gastrectomized rats develop calcium deficiency for some reason other than lack of acid. This possibility was tested in a study in which gastrectomized (and sham-operated) rats received CaCl₂ (100mg/kg/day) by continuous subcutaneous infusion for 4 weeks (osmotic minipumps). The calcium dose given represents approximately 20% of the daily requirement of calcium in young male rats. The calcium supplementation did not prevent the bone loss after gastrectomy. The results show that the stomach is important for calcium homeostasis and that the consequences of gastrectomy are probably not related to calcium malabsorption or calcium deficiency.

Key Words:

• Bone calcium
• bone density
• bone loss
• gastrectomy
• gastrocalcin